With the rapid development of integrated circuit (IC) technology, the size of the semiconductor devices of ICs, especially the metal oxide semiconductor (MOS) devices, has become smaller and smaller to match the requirements of device miniaturization and integration. When the size of the MOS transistor is continually shrunk, the process using the gate dielectric layer made of silicon oxide or silicon nitride meets certain challenges. For example, the transistors having the gate dielectric layer made of silicon oxide and silicon nitride face certain problems, such as the increase of leakage current, and/or the diffusion of the impurities, etc. Such problems may affect the threshold voltage of the transistors; and the performance of the semiconductor devices may be significantly affected.
In order to solve the above-mentioned problems, a high-K metal gate (HKMG) structure) has been introduced into the MOS transistors. The HKMG structure utilizes a high dielectric constant (high-K) material to substitute the conventionally used gate dielectric material, such as silicon oxide and silicon nitride, etc. The HKMG structure may reduce the leakage current of the transistor when the size of the transistor is reduced; and the performance of the transistor may be improved as well.
However, when the technical node of semiconductor process is further reduced, the size of transistors having HKMG structures is consistently reduced; and the device density is continuously increased, thus it may be difficult to control the fabrication process of the HKMG structures; and the performance of the transistors having the HKMG structures may be unstable. The disclosed device structures and methods are directed to solve one or more problems set forth above and other problems.